New chapters are released monthly, with official translations coming out at the 8th/9th of every month on Crunchyroll. Note the "Next Simulpub" time on the right.

Why does the new chapter say the next won't be for two months?

The issues are titled a month ahead. The January issue comes out in December, February in January, and so on.

Where can I see all the episode/chapter discussion threads posted on this subreddit?

Links to nearly all of the subreddit discussion threads for the anime, the manga, and its respective spin-offs are compiled here (table provided by /u/hoochiex21).

When will the series end?

In September 2013, Isayama mentioned that his aim was 20 volumes (82 chapters, ETA: June 9, 2016). In August 2014, an interview with his editor suggested the series may end in three to four years. Making 25 volumes (102 chapters, ETA: February 9, 2018) a more likely estimate. This equals to 3 seasons for the anime, assuming there will be ~33 chapters' worth of content per season.

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